In living environments surrounded by various electrical and electronic devices, batteries (cells), which generate electrical energy through physical or chemical reactions and supply power to the outside, are used when it is impossible to obtain AC power, which is supplied to buildings, or when DC power is required.
Among such batteries, primary batteries and secondary batteries, which are chemical batteries that use chemical reactions, are typically widely used, and the primary batteries, which are widely called dry batteries, are consumable batteries. Moreover, the secondary batteries are rechargeable batteries manufactured using materials in which redox reactions between a current and a material may be repeated numerous times. When a reduction reaction of the material is carried out by the current, power is charged, and when an oxidation reaction of the material is carried out, power is discharged. Electricity is generated as such charging-discharging is repeatedly performed.
Meanwhile, among the secondary batteries, lithium ion batteries are manufactured by accommodating and sealing in a cylindrical or angular can, pouch, etc., an electrode assembly, which is manufactured by coating an active material to a certain thickness on each of a positive electrode conductive foil and a negative electrode conductive foil, and then winding numerous times into a jelly roll or cylindrical shape such that a separation film is interposed between the two conductive foils.
Korean Patent Publication No. 10-2008-0037867 discloses a typical electrode assembly, a lithium secondary battery using the same, and a method for manufacturing the lithium secondary battery.
In a typical secondary battery, in order to manufacture an electrode, an active material is coated onto an electrode sheet using a stripe coating technique, and then the active material coating part is rolled.
FIG. 5 is a front view illustrating a typical electrode sheet.
As illustrated in FIG. 5, a coated part 3, which is coated with an active material, and an uncoated part 4, which is not coated with the active material, are formed on an electrode sheet 2.
However, the coating load of the coated part 3 varies according to the distance from the uncoated part 4, and thus there is a limitation in that the thickness of the active material in the coated part 3 is not uniform in a battery.
There is a limitation wherein lithium precipitation on the upper end of the battery and degradation of battery performance occur when balance between the positive electrode and the negative electrode is not achieved due to such a level of variation in active material loading in the electrode.
Moreover, there is a limitation wherein the non-uniformity in the thickness of the electrode itself increases electrode swelling.